Catalytic processes for hydrogenation of carbonyl groups in organic compounds such as esters, diesters, aldehydes or ketones are of great relevance in industry. They serve, inter alia, to convert carboxylic acids or their esters, specifically esters of fatty acids, to the corresponding alcohols.
Suitable catalysts here are systems based on copper in combination with further transition metal elements. The catalysts are typically in the form of tablets, extrudates or pellets.
WO 2004/085356 describes the preparation of a catalyst for the hydrogenation of carbonyl compounds which comprises, as well as copper and aluminum, at least one oxide of lanthanum, tungsten, molybdenum, titanium or zirconium, and to which have additionally been added copper powder or flakes, cement powder or graphite.
U.S. Pat. No. 6,020,285 describes the preparation of a cobalt- or nickel-containing catalyst also comprising calcium aluminate with an Al/Ca ratio of greater than 2.5. The catalyst is suitable for breakdown of hypochlorite.
WO 98/11985 discloses cobalt- or nickel-containing catalysts additionally comprising calcium aluminate with an Al/Ca ratio of greater than 4.0, and also alumina and/or magnesia. The catalyst is suitable for breakdown of oxidizing substances.
U.S. Pat. No. 7,084,312 describes the preparation of catalysts based on copper, zinc and aluminum, for which an oxidic mixture of copper, zinc and aluminum is blended with metallic copper, a cement or a mixture of the two materials and shaped to tablets. The catalyst is used for the hydrogenation of organic compounds having carbonyl groups.
Yakerson et al. (Scientific Bases for the Preparation of Heterogeneous Catalysts, Preparation of Catalysts, p. 879 ff.) describes the preparation of cement-containing metal catalysts, for example nickel, copper or zinc catalysts. The corresponding metal hydroxo carbonates are used for this purpose.
The starting compounds in the hydrogenation processes generally include traces of acidic compounds. These are, for example, carboxylic acids present as by-products in esterification reactions. These compounds attack the catalyst under the conditions of the hydrogenation reaction and lead to lowering of mechanical stability and the occasional observation of leaching-out of the catalytically active metals, which are discharged from the reaction reactor with the product stream and have to be separated therefrom. Moreover, there is also a reduction in the catalytic activity of the catalyst with advancing discharge of the catalytically active metals.
Catalysts containing copper and chromium are used for such reactions. These typically have elevated stability to the action of acid. Owing to stricter environmental regulations, the use of chromium catalysts is associated with ever higher demands, and so there is a need to replace the existing CuCr systems with environmentally compatible alternatives that nevertheless have comparable catalytic and physical properties.
It was therefore an object of the present invention to provide a catalyst for hydrogenations of carbonyl groups in organic compounds that features improved mechanical stability and is less prone to the action of acidic compounds.
This object is achieved by the catalyst of the invention.